Sounds to be a really smart choice. Be sure to bolt those 6x6s together, I would use a 1/2" X 10" hex bolt with washers, and recess the end in. One bolt, centered, ever two feet, or so. The reason being, if you skip that step and do a nice column wrap, at least one of those 6x6s will decide to bow away from the group and bust the wrap apart. If you have a battery impact driver, you could also clamp them together with some of the 10" timber screws used for landscape ties, and deck building. I would install these in pairs, though.